People often use the terms “jail” and “prison” interchangeably. This makes sense to some degree because they have functions that are somewhat similar to one another. However, they are not the same thing. Jails are more of short term institutions whereas prisons are for the long term.
Of course, both of these types of facilities perform similar functions. Both of them are meant to house people in a secure way so that they cannot escape. Both of them are meant to confine those people for legal reasons.
Beyond that, there are important differences. Jails are used for two purposes. First, people are typically held in a jail while they are awaiting trial. Many people in jails, then, have not been convicted of a crime. Jails are, therefore, a first point of entry into the system for people who have been arrested. Their staff has to deal with people who are just coming in off the street and may have various problems that will need to be addressed if they are to be safely housed. Jails are also used to house those convicted of relatively minor offenses. For example, people serving terms of less than a year are often held in jails.
By contrast, prisons are where people are sent after they have been convicted of crimes. Prisons are facilities where convicts are incarcerated for relatively long periods of time. Their main function is to control people who are long-term inmates.
Thus, while jails and prisons are similar in some ways, they are very different in others.